Electrical line

ABSTRACT

An improved electrical line comprising an electrical conductor ( 5 ) and a layer of thermoplastic material wherein the layer consists of at least one inner layer ( 6 ) and one outer layer ( 7 ) and the outer layer ( 7 ) comprises a lubricant which has migrated from the inner layer ( 6 ) into the outer layer ( 7 ).

RELATED APPLICATION

The present application is related to and claims the benefit of priorityfrom European Patent Application No. 06290431.3, filed on Mar. 15, 2006,the entirety of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an electrical line, in particular anelectrical line to be laid in cable ducts.

BACKGROUND

In order to reduce the time of installation of electrical lines in ductsit is very important, to reduce friction between the electrical line andthe inner surface of the cable duct.

From WO 02/39560 A1 it is known to apply a friction-reducing layer tothe inner surface of the duct. The friction-reducing layer is alubricating particulate solid phase, which includes carbon black and alubricating plastic material.

WO 2004/114489 A1 discloses a tube for installation of flexible cables.The tube comprises an outer layer of low-density polyethylene and aninner layer of high-density polyethylene containing a blend of polyamideand polyether block amides with a silicone slip agent.

On the other hand it is known to reduce the friction by providing theouter surface of the outermost layer (the sheath) with longitudinal orhelical ribs. Such a solution is described in DE 8901210 U1.

JP 01089210A proposes a cable to be pulled into a duct wherein alubricant layer for reducing a friction coefficient of the cable and arip cord for tearing an outer sheath are interposed between an innersheath and the outer sheath. When tearing off the outer sheath with therip cord the friction coefficient between the inner sheath and the ductline inner wall is lowered by the lubricant layer. Thus, the cable canbe introduced smoothly into the duct line without adding surplus tensionto it.

Still another solution of the described problem is object of JP02123622. To improve the self-lubricating ability a resin film layer isobtained by adding a predetermined amount of a specific lubricant to theinsulating layer on a conductor. For instance 0.2-5.0 weight part ofalkylphenoxypoly (ethylene oxide) ethanole are added to 100 weight partof the insulating resin.

One main problem of this solution is the compatibily between theslipperiness and the coil packaging film. It is not possible to move thecoil of the electrical line provided with the lubricant without rigidboxes. This is a main drawback for the producer of such electricallines.

OBJECTS AND SUMMARY

The object of the present invention is therefore that of providing anelectrical line (or cable) with a layer, which is not slipperyimmediately after the production but which has a lubricating layerbefore it is drawn into ducts.

This object is achieved by the fact that the line comprises an innerlayer and an outer layer and that the outer layer comprises a lubricantwhich has migrated from the inner layer into the outer layer.

Preferably the said lubricant is a wax of the group of fatty acidamides.

By way of example one can cite behenamide, oleamide, stearamide,erucamide, oleyl palmitamide, stearyl or ethylene bis-stearamide as awax of the group of fatty acid amides.

According to a further embodiment of the invention the thermoplasticmaterial of the inner layer is a halogene free, flame retardant compoundbased on copolymers of ethylene, as for instance Ethylene vinyl acetate(EVA).

The thermoplastic material of the outer layer may be the same materialas for the inner layer. A polypropylene compound can be used bypreference, too.

In a further preferred embodiment the ratio of the wall thickness of theinner and the outer layer is between 50:50 and 95:5.

The outer layer may be coloured in order to distinguish the lines, whenmore than one lines are positioned in one duct.

In a first embodiment the inner layer of thermoplastic material isextruded to the electrical conductor, whereby this material contains alubricant, the outer layer is extruded to the inner layer, whereby thelubricant migrates at least partly from the inner layer to the outerlayer over a period of at least two days, preferably at least one week.

The thermoplastic material of the inner layer is compounded with thelubricant and granulated.

Preferably the inner and the outer layer are coextruded.

In a further possibility of producing an electrical line according tothe invention the inner layer of thermoplastic material is extruded tothe conductor, the lubricant is applied to the inner layer and the outerlayer is extruded to the inner layer coated with the lubricant. Thelubricant will migrate at least partly from the surface of the innerlayer into the outer layer in a period of time between two days and oneweek. The lubricant is applied to the inner layer preferably byspraying.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the present invention willbecome apparent from the following detailed description, made withreference to the attached drawings provided purely by way offnon-limitative example, in which

FIG. 1 is a view of a cable duct with three electrical lines therein and

FIG. 2 is a view of an electrical line according to the invention.

DETAILED DESCRIPTION

In FIG. 1 three electrical lines 1, 2 and 3 are pulled into a cable duct4. Each of the electrical lines 1, 2 and 3 has a layer 8 of lubricant ontheir outer surface in order to reduce friction between the innersurface of the cable duct 4 and the outer surface of the electricallines 1, 2 and 3 during the installation of the electrical lines 1, 2and 3 in the cable duct 4.

One embodiment of the invention is show in FIG. 2.

The electrical line comprises an electrical conductor 5 consisting of aplurality of twisted wires for example of copper or aluminium.Proceeding outwardly, the electrical conductor 5 is successivelysurrounded by a first inner layer 6 and a second outer layer 7.

The inner layer 6 and the outer layer 7 are produced by coextrusion.

Alternatively the inner layer 6 may be extruded first to the electricalconductor 5, then a wax of the group of fatty acid amides is applied tothe outer surface of the inner layer 6 and at last the outer layer 7 isextruded to the inner layer 6.

Preferably layers 6 and 7 consist of a halogene free, flame retardantcompound based on copolymers of ethylene. Alternatively the outer layer7 may consist of a polypropylene compound.

A mixture used for the inner layer 6 and preferably for the layer 7 hasfor example the following formulation: parts by weight EVA-Copolymer 60PE-LL 30 PE-MAH grafted 10 Aluminiumhydroxide 150 Antioxidant 1 Searylbis-stearamide 0.5

The preferred materials for the EVA-Copolymer and the PE-LL areavailable from Exxon Chemical Co designated as “Escorene UL”, and“Escorene LL”. PW-MAH-grafted is available from Dupont and designated as“Fusabond”.

A mixture used for the outer layer 7 has the same formulation butwithout Searyl bis-stearamide.

The Searyl bis-stearamide will migrate from the inner layer 6 or fromthe coating of the inner layer 6 into the outer layer 7 and will form alubricating layer 8 on the surface of the outer layer 7.

The lubricant should not become effective on the surface of the layer 7before one week and should be finished after four weeks.

The migration speed depends on the temperature in the layers 6 and 7,the concentration of the lubricant in the layers 6 and 7 and the wallthickness of the layers 6 and 7, especially of the layer 7. Thereforethe ratio of the wall thicknesses of the layers 6 and 7 should be in therange of 50:50 and 95:5.

When more than one electrical lines 1, 2 or 3 have been installed in theduct 4 it is necessary to make it possible to identity the electricallines. Therefore the outer layer 7 of the electrical line is coloured.

1. Electrical line comprising: an electrical conductor; and a layer ofthermoplastic material, wherein the layer consists of at least one innerlayer and one outer layer and the outer layer has a lubricant which hasmigrated from the inner layer into the outer layer.
 2. Electrical lineaccording to claim 1, wherein the lubricant is a wax of the group offatty acid amides.
 3. Electrical line according to claim 1, wherein thethermoplastic material of the inner layer is a halogen free, flameretardant compound based on copolymers of ethylene.
 4. Electrical lineaccording to claim 1, wherein the thermoplastic material of the outerlayer is a halogen free, flame retardant compound based on copolymers ofethylene.
 5. Electrical line according to claim 1, wherein thethermoplastic material of the outer layer is a polypropylene compound.6. Electrical line according to claim 1, wherein the ratio of thewallthicknesses of the inner layer and the outer layer is between 50:50to 95:5.
 7. Electrical line according to claim 1, wherein the outerlayer is coloured.
 8. Method of producing an electrical line accordingto claim 1, wherein the inner layer of thermoplastic material isextruded to the electrical conductor, whereby the thermoplastic materialcontains a lubricant, that the outer layer is extruded to the innerlayer and whereby the lubricant migrates at least partly from the innerlayer to the outer layer over a period of at least two days, preferablyat least one week.
 9. Method of producing an electrical line accordingto claim 8, wherein the inner layer and the outer layer are co-extruded.10. Method of producing an electrical line according to claim 1, whereinthe thermoplastic material of the inner layer is extruded to theelectrical conductor, the lubricant is applied to the surface of theinner layer and the thermoplastic material of the outer layer isextruded to the inner layer which is coated with the lubricant wherebythe lubricant migrates into the outer layer over a period of at leasttwo days, preferably at least one week.